Discussions have been in progress on a home base station Home-eNB in RAN-WG of the “LTE (Long Term Evolution)” in the 3GPP (3rd Generation Partnership Project).
Specifically, according to the current 3GPP specifications, a mobile communication system is configured to manage a specific mobile station (a specific mobile station which is allowed to communicating through a specific cell) belonging to a CSG (Closed Subscriber Group) under the control of a home base station Home-eNB or a macro base station eNB.
In other words, according to the current 3GPP specifications, only a specific mobile station belonging to a CSG is configured to be capable of communicating through the CSG cell (the specific cell) under the control of the home base station Home-eNB or the macro base station eNB.
However, in the current 3GPP specifications, even when a general mobile station other than the specific mobile station cannot detect a cell fulfilling a predetermined radio condition, except for the CSG cell, the general mobile station cannot perform a communication through the CSG cell.
In general, the home base station Home-eNB is supposed to be installed inside a building and is also supposed to be installed in a place where radio waves from the macro base station eNB installed outside buildings in the public wireless network are not detected. Accordingly, as described above, it is believed that there often occurs a situation in which a general mobile station other than the specific mobile station cannot detect a cell fulfilling a predetermined radio condition except for the CSG cell under the control of the home base station Home-eNB.
In such a case, even when there are available radio resources left in the CSG cell, the general mobile station cannot use the CSG cell as a camped cell and becomes out of service.
Meanwhile, when many CSG cells are operated at the same frequency band as that of the public wireless network (a macro cell), there arises a problem of mutual interference.
For example, when a mobile station without an access right to the CSG cell performs a communication with a macro cell in a place close to the CSG cell having a less transmission loss, an uplink interference with the CSG cell is considerably increased.
In contrast, in a downlink communication of the mobile station, an interference from the radio waves from the CSG cell occurs, and thus a communication quality is considerably deteriorated.
Meanwhile, when many CSG cells are operated at a frequency band different from that of the macro cell, there arises a problem of interference between the different CSG cells.
In particular, the home base station is supposed to be installed by an end user, and therefore a cell designing is supposed not to be sufficiently made. Accordingly, the mutual interference between the CSG cells can be a serious problem.